The sun rises, the night turns into a day, the seasons change, the leaves shed, flowers bloom and living beings grow! Every day, we see a number of changes happening around us. Change is inevitable. It takes place all the time and everywhere. However, changes differ from one another in a number of aspects. Some changes are fast, others are slow. Some of them are temporary, others are permanent.
Some are periodic, others are non-periodic. Some are natural, others are man-made. Some are reversible, others are irreversible. On the larger front, a change may be categorized into a chemical or a physical change depending on how the properties of a subject alter when it undergoes the change.
A substance is said to undergo a physical change when only the physical properties such as the shape, size, colour, state or appearance of the substance change. Its chemical composition remains intact. Some characteristics of a physical change are:
- Temporary in nature.
- Does not affect the internal structure of a substance, only the molecules are rearranged.
- No new substance is formed.
- Most of the physical changes are reversible. We can obtain the substance back even after the change.
Some examples of a physical change are folding of a paper sheet, melting of wax, freezing and boiling water, melting of ice, condensation, vaporization, magnetizing a compass needle, dissolving sugar in water, etc.
A substance is said to undergo a chemical change when the chemical properties of a substance alter. As a result, there is either formation or breaking of atomic bonds at the molecular level. Some characteristics of a chemical change are:
- Permanent in nature.
- Since the original composition of the substance changes, one or more new substances are formed.
- Forms of energy, such as heat, light or electricity, may be emitted or absorbed.
- A chemical change is generally irreversible. At least, it cannot be reversed by simple physical means.
Some examples of a chemical change are burning of paper, burning of fuel, rusting of iron, the souring of milk, growth in a living being, cooking, digestion of food, burning of wood, etc.
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